<?php

//
// Markdown Parser Interface
//

interface MarkdownInterface
{
    //
    // Initialize the parser and return the result of its transform method.
    // This will work fine for derived classes too.
    //
    public static function defaultTransform($text);

    //
    // Main function. Performs some preprocessing on the input text
    // and pass it through the document gamut.
    //
    public function transform($text);
}

//
// Markdown Parser Class
//

class Markdown implements MarkdownInterface
{
    //## Version ###

    const  MARKDOWNLIB_VERSION = "1.4.1";

    //## Simple Function Interface ###

    public static function defaultTransform($text)
    {
        //
        // Initialize the parser and return the result of its transform method.
        // This will work fine for derived classes too.
        //
        // Take parser class on which this function was called.
        $parser_class = get_called_class();

        // try to take parser from the static parser list
        static $parser_list;
        $parser = &$parser_list[$parser_class];

        // create the parser it not already set
        if (!$parser) {
            $parser = new $parser_class();
        }

        // Transform text using parser.
        return $parser->transform($text);
    }

    //## Configuration Variables ###

    // Change to ">" for HTML output.
    public $empty_element_suffix = " />";
    public $tab_width = 4;

    // Change to `true` to disallow markup or entities.
    public $no_markup = false;
    public $no_entities = false;

    // Predefined urls and titles for reference links and images.
    public $predef_urls = array();
    public $predef_titles = array();

    // Optional filter function for URLs
    public $url_filter_func = null;

    //## Parser Implementation ###

    // Regex to match balanced [brackets].
    // Needed to insert a maximum bracked depth while converting to PHP.
    protected $nested_brackets_depth = 6;
    protected $nested_brackets_re;

    protected $nested_url_parenthesis_depth = 4;
    protected $nested_url_parenthesis_re;

    // Table of hash values for escaped characters:
    protected $escape_chars = '\`*_{}[]()>#+-.!';
    protected $escape_chars_re;

    public function __construct()
    {
        //
        // Constructor function. Initialize appropriate member variables.
        //
        $this->_initDetab();
        $this->prepareItalicsAndBold();

        $this->nested_brackets_re =
            str_repeat('(?>[^\[\]]+|\[', $this->nested_brackets_depth) .
            str_repeat('\])*', $this->nested_brackets_depth);

        $this->nested_url_parenthesis_re =
            str_repeat('(?>[^()\s]+|\(', $this->nested_url_parenthesis_depth) .
            str_repeat('(?>\)))*', $this->nested_url_parenthesis_depth);

        $this->escape_chars_re = '[' . preg_quote($this->escape_chars) . ']';

        // Sort document, block, and span gamut in ascendent priority order.
        asort($this->document_gamut);
        asort($this->block_gamut);
        asort($this->span_gamut);
    }

    // Internal hashes used during transformation.
    protected $urls = array();
    protected $titles = array();
    protected $html_hashes = array();

    // Status flag to avoid invalid nesting.
    protected $in_anchor = false;

    protected function setup()
    {
        //
        // Called before the transformation process starts to setup parser
        // states.
        //
        // Clear global hashes.
        $this->urls = $this->predef_urls;
        $this->titles = $this->predef_titles;
        $this->html_hashes = array();

        $this->in_anchor = false;
    }

    protected function teardown()
    {
        //
        // Called after the transformation process to clear any variable
        // which may be taking up memory unnecessarly.
        //
        $this->urls = array();
        $this->titles = array();
        $this->html_hashes = array();
    }

    public function transform($text)
    {
        //
        // Main function. Performs some preprocessing on the input text
        // and pass it through the document gamut.
        //
        $this->setup();

        // Remove UTF-8 BOM and marker character in input, if present.
        $text = preg_replace('{^\xEF\xBB\xBF|\x1A}', '', $text);

        // Standardize line endings:
        //   DOS to Unix and Mac to Unix
        $text = preg_replace('{\r\n?}', "\n", $text);

        // Make sure $text ends with a couple of newlines:
        $text .= "\n\n";

        // Convert all tabs to spaces.
        $text = $this->detab($text);

        // Turn block-level HTML blocks into hash entries
        $text = $this->hashHTMLBlocks($text);

        // Strip any lines consisting only of spaces and tabs.
        // This makes subsequent regexen easier to write, because we can
        // match consecutive blank lines with /\n+/ instead of something
        // contorted like /[ ]*\n+/ .
        $text = preg_replace('/^[ ]+$/m', '', $text);

        // Run document gamut methods.
        foreach ($this->document_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        $this->teardown();

        return $text . "\n";
    }

    protected $document_gamut = array(
        // Strip link definitions, store in hashes.
        "stripLinkDefinitions" => 20,

        "runBasicBlockGamut"   => 30,
    );

    protected function stripLinkDefinitions($text)
    {
        //
        // Strips link definitions from text, stores the URLs and titles in
        // hash references.
        //
        $less_than_tab = $this->tab_width - 1;

        // Link defs are in the form: ^[id]: url "optional title"
        $text = preg_replace_callback(
            '{
							^[ ]{0,' . $less_than_tab . '}\[(.+)\][ ]?:	# id = $1
							  [ ]*
							  \n?				# maybe *one* newline
							  [ ]*
							(?:
							  <(.+?)>			# url = $2
							|
							  (\S+?)			# url = $3
							)
							  [ ]*
							  \n?				# maybe one newline
							  [ ]*
							(?:
								(?<=\s)			# lookbehind for whitespace
								["(]
								(.*?)			# title = $4
								[")]
								[ ]*
							)?	# title is optional
							(?:\n+|\Z)
			}xm',
            array($this, '_stripLinkDefinitions_callback'),
            $text
        );

        return $text;
    }

    protected function _stripLinkDefinitions_callback($matches)
    {
        $link_id = strtolower($matches[1]);
        $url = $matches[2] == '' ? $matches[3] : $matches[2];
        $this->urls[$link_id] = $url;
        $this->titles[$link_id] = &$matches[4];

        return ''; // String that will replace the block
    }

    protected function hashHTMLBlocks($text)
    {
        if ($this->no_markup) {
            return $text;
        }

        $less_than_tab = $this->tab_width - 1;

        // Hashify HTML blocks:
        // We only want to do this for block-level HTML tags, such as headers,
        // lists, and tables. That's because we still want to wrap <p>s around
        // "paragraphs" that are wrapped in non-block-level tags, such as anchors,
        // phrase emphasis, and spans. The list of tags we're looking for is
        // hard-coded:
        //
        // *  List "a" is made of tags which can be both inline or block-level.
        //    These will be treated block-level when the start tag is alone on
        //    its line, otherwise they're not matched here and will be taken as
        //    inline later.
        // *  List "b" is made of tags which are always block-level;
        //
        $block_tags_a_re = 'ins|del';
        $block_tags_b_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|' .
                           'script|noscript|style|form|fieldset|iframe|math|svg|' .
                           'article|section|nav|aside|hgroup|header|footer|' .
                           'figure';

        // Regular expression for the content of a block tag.
        $nested_tags_level = 4;
        $attr = '
			(?>				# optional tag attributes
			  \s			# starts with whitespace
			  (?>
				[^>"/]+		# text outside quotes
			  |
				/+(?!>)		# slash not followed by ">"
			  |
				"[^"]*"		# text inside double quotes (tolerate ">")
			  |
				\'[^\']*\'	# text inside single quotes (tolerate ">")
			  )*
			)?	
			';
        $content =
            str_repeat('
				(?>
				  [^<]+			# content without tag
				|
				  <\2			# nested opening tag
					' . $attr . '	# attributes
					(?>
					  />
					|
					  >', $nested_tags_level) .    // end of opening tag
                      '.*?' .                    // last level nested tag content
            str_repeat(
                '
					  </\2\s*>	# closing nested tag
					)
				  |				
					<(?!/\2\s*>	# other tags with a different name
				  )
				)*',
                $nested_tags_level
            );
        $content2 = str_replace('\2', '\3', $content);

        // First, look for nested blocks, e.g.:
        // 	<div>
        // 		<div>
        // 		tags for inner block must be indented.
        // 		</div>
        // 	</div>
        //
        // The outermost tags must start at the left margin for this to match, and
        // the inner nested divs must be indented.
        // We need to do this before the next, more liberal match, because the next
        // match will start at the first `<div>` and stop at the first `</div>`.
        $text = preg_replace_callback(
            '{(?>
			(?>
				(?<=\n)			# Starting on its own line
				|				# or
				\A\n?			# the at beginning of the doc
			)
			(						# save in $1

			  # Match from `\n<tag>` to `</tag>\n`, handling nested tags 
			  # in between.
					
						[ ]{0,' . $less_than_tab . '}
						<(' . $block_tags_b_re . ')# start tag = $2
						' . $attr . '>			# attributes followed by > and \n
						' . $content . '		# content, support nesting
						</\2>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document

			| # Special version for tags of group a.

						[ ]{0,' . $less_than_tab . '}
						<(' . $block_tags_a_re . ')# start tag = $3
						' . $attr . '>[ ]*\n	# attributes followed by >
						' . $content2 . '		# content, support nesting
						</\3>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document
					
			| # Special case just for <hr />. It was easier to make a special 
			  # case than to make the other regex more complicated.
			
						[ ]{0,' . $less_than_tab . '}
						<(hr)				# start tag = $2
						' . $attr . '			# attributes
						/?>					# the matching end tag
						[ ]*
						(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # Special case for standalone HTML comments:
			
					[ ]{0,' . $less_than_tab . '}
					(?s:
						<!-- .*? -->
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # PHP and ASP-style processor instructions (<? and <%)
			
					[ ]{0,' . $less_than_tab . '}
					(?s:
						<([?%])			# $2
						.*?
						\2>
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
					
			)
			)}Sxmi',
            array($this, '_hashHTMLBlocks_callback'),
            $text
        );

        return $text;
    }

    protected function _hashHTMLBlocks_callback($matches)
    {
        $text = $matches[1];
        $key = $this->hashBlock($text);

        return "\n\n$key\n\n";
    }

    protected function hashPart($text, $boundary = 'X')
    {
        //
        // Called whenever a tag must be hashed when a function insert an atomic
        // element in the text stream. Passing $text to through this function gives
        // a unique text-token which will be reverted back when calling unhash.
        //
        // The $boundary argument specify what character should be used to surround
        // the token. By convension, "B" is used for block elements that needs not
        // to be wrapped into paragraph tags at the end, ":" is used for elements
        // that are word separators and "X" is used in the general case.
        //
        // Swap back any tag hash found in $text so we do not have to `unhash`
        // multiple times at the end.
        $text = $this->unhash($text);

        // Then hash the block.
        static $i = 0;
        $key = "$boundary\x1A" . ++$i . $boundary;
        $this->html_hashes[$key] = $text;

        return $key; // String that will replace the tag.
    }

    protected function hashBlock($text)
    {
        //
        // Shortcut function for hashPart with block-level boundaries.
        //
        return $this->hashPart($text, 'B');
    }

    protected $block_gamut = array(
        //
        // These are all the transformations that form block-level
        // tags like paragraphs, headers, and list items.
        //
        "doHeaders"         => 10,
        "doHorizontalRules" => 20,

        "doLists"           => 40,
        "doCodeBlocks"      => 50,
        "doBlockQuotes"     => 60,
    );

    protected function runBlockGamut($text)
    {
        //
        // Run block gamut tranformations.
        //
        // We need to escape raw HTML in Markdown source before doing anything
        // else. This need to be done for each block, and not only at the
        // begining in the Markdown function since hashed blocks can be part of
        // list items and could have been indented. Indented blocks would have
        // been seen as a code block in a previous pass of hashHTMLBlocks.
        $text = $this->hashHTMLBlocks($text);

        return $this->runBasicBlockGamut($text);
    }

    protected function runBasicBlockGamut($text)
    {
        //
        // Run block gamut tranformations, without hashing HTML blocks. This is
        // useful when HTML blocks are known to be already hashed, like in the first
        // whole-document pass.
        //
        foreach ($this->block_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        // Finally form paragraph and restore hashed blocks.
        $text = $this->formParagraphs($text);

        return $text;
    }

    protected function doHorizontalRules($text)
    {
        // Do Horizontal Rules:
        return preg_replace(
            '{
				^[ ]{0,3}	# Leading space
				([-*_])		# $1: First marker
				(?>			# Repeated marker group
					[ ]{0,2}	# Zero, one, or two spaces.
					\1			# Marker character
				){2,}		# Group repeated at least twice
				[ ]*		# Tailing spaces
				$			# End of line.
			}mx',
            "\n" . $this->hashBlock("<hr$this->empty_element_suffix") . "\n",
            $text
        );
    }

    protected $span_gamut = array(
        //
        // These are all the transformations that occur *within* block-level
        // tags like paragraphs, headers, and list items.
        //
        // Process character escapes, code spans, and inline HTML
        // in one shot.
        "parseSpan"           => -30,

        // Process anchor and image tags. Images must come first,
        // because ![foo][f] looks like an anchor.
        "doImages"            => 10,
        "doAnchors"           => 20,

        // Make links out of things like `<http://example.com/>`
        // Must come after doAnchors, because you can use < and >
        // delimiters in inline links like [this](<url>).
        "doAutoLinks"         => 30,
        "encodeAmpsAndAngles" => 40,

        "doItalicsAndBold"    => 50,
        "doHardBreaks"        => 60,
    );

    protected function runSpanGamut($text)
    {
        //
        // Run span gamut tranformations.
        //
        foreach ($this->span_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        return $text;
    }

    protected function doHardBreaks($text)
    {
        // Do hard breaks:
        return preg_replace_callback(
            '/ {2,}\n/',
            array($this, '_doHardBreaks_callback'),
            $text
        );
    }

    protected function _doHardBreaks_callback($matches)
    {
        return $this->hashPart("<br$this->empty_element_suffix\n");
    }

    protected function doAnchors($text)
    {
        //
        // Turn Markdown link shortcuts into XHTML <a> tags.
        //
        if ($this->in_anchor) {
            return $text;
        }
        $this->in_anchor = true;

        //
        // First, handle reference-style links: [link text] [id]
        //
        $text = preg_replace_callback(
            '{
			(					# wrap whole match in $1
			  \[
				(' . $this->nested_brackets_re . ')	# link text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'),
            $text
        );

        //
        // Next, inline-style links: [link text](url "optional title")
        //
        $text = preg_replace_callback(
            '{
			(				# wrap whole match in $1
			  \[
				(' . $this->nested_brackets_re . ')	# link text = $2
			  \]
			  \(			# literal paren
				[ \n]*
				(?:
					<(.+?)>	# href = $3
				|
					(' . $this->nested_url_parenthesis_re . ')	# href = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# Title = $7
				  \6		# matching quote
				  [ \n]*	# ignore any spaces/tabs between closing quote and )
				)?			# title is optional
			  \)
			)
			}xs',
            array($this, '_doAnchors_inline_callback'),
            $text
        );

        //
        // Last, handle reference-style shortcuts: [link text]
        // These must come last in case you've also got [link text][1]
        // or [link text](/foo)
        //
        $text = preg_replace_callback(
            '{
			(					# wrap whole match in $1
			  \[
				([^\[\]]+)		# link text = $2; can\'t contain [ or ]
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'),
            $text
        );

        $this->in_anchor = false;

        return $text;
    }

    protected function _doAnchors_reference_callback($matches)
    {
        $whole_match = $matches[1];
        $link_text = $matches[2];
        $link_id = &$matches[3];

        if ($link_id == "") {
            // for shortcut links like [this][] or [this].
            $link_id = $link_text;
        }

        // lower-case and turn embedded newlines into spaces
        $link_id = strtolower($link_id);
        $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

        if (isset($this->urls[$link_id])) {
            $url = $this->urls[$link_id];
            $url = $this->encodeURLAttribute($url);

            $result = "<a href=\"$url\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .= " title=\"$title\"";
            }

            $link_text = $this->runSpanGamut($link_text);
            $result .= ">$link_text</a>";
            $result = $this->hashPart($result);
        } else {
            $result = $whole_match;
        }

        return $result;
    }

    protected function _doAnchors_inline_callback($matches)
    {
        $whole_match = $matches[1];
        $link_text = $this->runSpanGamut($matches[2]);
        $url = $matches[3] == '' ? $matches[4] : $matches[3];
        $title = &$matches[7];

        // if the URL was of the form <s p a c e s> it got caught by the HTML
        // tag parser and hashed. Need to reverse the process before using the URL.
        $unhashed = $this->unhash($url);
        if ($unhashed != $url) {
            $url = preg_replace('/^<(.*)>$/', '\1', $unhashed);
        }

        $url = $this->encodeURLAttribute($url);

        $result = "<a href=\"$url\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .= " title=\"$title\"";
        }

        $link_text = $this->runSpanGamut($link_text);
        $result .= ">$link_text</a>";

        return $this->hashPart($result);
    }

    protected function doImages($text)
    {
        //
        // Turn Markdown image shortcuts into <img> tags.
        //
        //
        // First, handle reference-style labeled images: ![alt text][id]
        //
        $text = preg_replace_callback(
            '{
			(				# wrap whole match in $1
			  !\[
				(' . $this->nested_brackets_re . ')		# alt text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]

			)
			}xs',
            array($this, '_doImages_reference_callback'),
            $text
        );

        //
        // Next, handle inline images:  ![alt text](url "optional title")
        // Don't forget: encode * and _
        //
        $text = preg_replace_callback(
            '{
			(				# wrap whole match in $1
			  !\[
				(' . $this->nested_brackets_re . ')		# alt text = $2
			  \]
			  \s?			# One optional whitespace character
			  \(			# literal paren
				[ \n]*
				(?:
					<(\S*)>	# src url = $3
				|
					(' . $this->nested_url_parenthesis_re . ')	# src url = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# title = $7
				  \6		# matching quote
				  [ \n]*
				)?			# title is optional
			  \)
			)
			}xs',
            array($this, '_doImages_inline_callback'),
            $text
        );

        return $text;
    }

    protected function _doImages_reference_callback($matches)
    {
        $whole_match = $matches[1];
        $alt_text = $matches[2];
        $link_id = strtolower($matches[3]);

        if ($link_id == "") {
            $link_id = strtolower($alt_text); // for shortcut links like ![this][].
        }

        $alt_text = $this->encodeAttribute($alt_text);
        if (isset($this->urls[$link_id])) {
            $url = $this->encodeURLAttribute($this->urls[$link_id]);
            $result = "<img src=\"$url\" alt=\"$alt_text\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .= " title=\"$title\"";
            }
            $result .= $this->empty_element_suffix;
            $result = $this->hashPart($result);
        } else {
            // If there's no such link ID, leave intact:
            $result = $whole_match;
        }

        return $result;
    }

    protected function _doImages_inline_callback($matches)
    {
        $whole_match = $matches[1];
        $alt_text = $matches[2];
        $url = $matches[3] == '' ? $matches[4] : $matches[3];
        $title = &$matches[7];

        $alt_text = $this->encodeAttribute($alt_text);
        $url = $this->encodeURLAttribute($url);
        $result = "<img src=\"$url\" alt=\"$alt_text\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .= " title=\"$title\""; // $title already quoted
        }
        $result .= $this->empty_element_suffix;

        return $this->hashPart($result);
    }

    protected function doHeaders($text)
    {
        // Setext-style headers:
        //	  Header 1
        //	  ========
        //
        //	  Header 2
        //	  --------
        //
        $text = preg_replace_callback(
            '{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
            array($this, '_doHeaders_callback_setext'),
            $text
        );

        // atx-style headers:
        //	# Header 1
        //	## Header 2
        //	## Header 2 with closing hashes ##
        //	...
        //	###### Header 6
        //
        $text = preg_replace_callback(
            '{
				^(\#{1,6})	# $1 = string of #\'s
				[ ]*
				(.+?)		# $2 = Header text
				[ ]*
				\#*			# optional closing #\'s (not counted)
				\n+
			}xm',
            array($this, '_doHeaders_callback_atx'),
            $text
        );

        return $text;
    }

    protected function _doHeaders_callback_setext($matches)
    {
        // Terrible hack to check we haven't found an empty list item.
        if ($matches[2] == '-' && preg_match('{^-(?: |$)}', $matches[1])) {
            return $matches[0];
        }

        $level = $matches[2][0] == '=' ? 1 : 2;
        $block = "<h$level>" . $this->runSpanGamut($matches[1]) . "</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }

    protected function _doHeaders_callback_atx($matches)
    {
        $level = strlen($matches[1]);
        $block = "<h$level>" . $this->runSpanGamut($matches[2]) . "</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }

    protected function doLists($text)
    {
        //
        // Form HTML ordered (numbered) and unordered (bulleted) lists.
        //
        $less_than_tab = $this->tab_width - 1;

        // Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re = '[*+-]';
        $marker_ol_re = '\d+[\.]';

        $markers_relist = array(
            $marker_ul_re => $marker_ol_re,
            $marker_ol_re => $marker_ul_re,
        );

        foreach ($markers_relist as $marker_re => $other_marker_re) {
            // Re-usable pattern to match any entirel ul or ol list:
            $whole_list_re = '
				(								# $1 = whole list
				  (								# $2
					([ ]{0,' . $less_than_tab . '})	# $3 = number of spaces
					(' . $marker_re . ')			# $4 = first list item marker
					[ ]+
				  )
				  (?s:.+?)
				  (								# $5
					  \z
					|
					  \n{2,}
					  (?=\S)
					  (?!						# Negative lookahead for another list item marker
						[ ]*
						' . $marker_re . '[ ]+
					  )
					|
					  (?=						# Lookahead for another kind of list
					    \n
						\3						# Must have the same indentation
						' . $other_marker_re . '[ ]+
					  )
				  )
				)
			'; // mx

            // We use a different prefix before nested lists than top-level lists.
            // See extended comment in _ProcessListItems().

            if ($this->list_level) {
                $text = preg_replace_callback(
                    '{
						^
						' . $whole_list_re . '
					}mx',
                    array($this, '_doLists_callback'),
                    $text
                );
            } else {
                $text = preg_replace_callback(
                    '{
						(?:(?<=\n)\n|\A\n?) # Must eat the newline
						' . $whole_list_re . '
					}mx',
                    array($this, '_doLists_callback'),
                    $text
                );
            }
        }

        return $text;
    }

    protected function _doLists_callback($matches)
    {
        // Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re = '[*+-]';
        $marker_ol_re = '\d+[\.]';
        $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

        $list = $matches[1];
        $list_type = preg_match("/$marker_ul_re/", $matches[4]) ? "ul" : "ol";

        $marker_any_re = ($list_type == "ul" ? $marker_ul_re : $marker_ol_re);

        $list .= "\n";
        $result = $this->processListItems($list, $marker_any_re);

        $result = $this->hashBlock("<$list_type>\n" . $result . "</$list_type>");

        return "\n" . $result . "\n\n";
    }

    protected $list_level = 0;

    protected function processListItems($list_str, $marker_any_re)
    {
        //
        //	Process the contents of a single ordered or unordered list, splitting it
        //	into individual list items.
        //
        // The $this->list_level global keeps track of when we're inside a list.
        // Each time we enter a list, we increment it; when we leave a list,
        // we decrement. If it's zero, we're not in a list anymore.
        //
        // We do this because when we're not inside a list, we want to treat
        // something like this:
        //
        //		I recommend upgrading to version
        //		8. Oops, now this line is treated
        //		as a sub-list.
        //
        // As a single paragraph, despite the fact that the second line starts
        // with a digit-period-space sequence.
        //
        // Whereas when we're inside a list (or sub-list), that line will be
        // treated as the start of a sub-list. What a kludge, huh? This is
        // an aspect of Markdown's syntax that's hard to parse perfectly
        // without resorting to mind-reading. Perhaps the solution is to
        // change the syntax rules such that sub-lists must start with a
        // starting cardinal number; e.g. "1." or "a.".

        $this->list_level++;

        // trim trailing blank lines:
        $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

        $list_str = preg_replace_callback(
            '{
			(\n)?							# leading line = $1
			(^[ ]*)							# leading whitespace = $2
			(' . $marker_any_re . '				# list marker and space = $3
				(?:[ ]+|(?=\n))	# space only required if item is not empty
			)
			((?s:.*?))						# list item text   = $4
			(?:(\n+(?=\n))|\n)				# tailing blank line = $5
			(?= \n* (\z | \2 (' . $marker_any_re . ') (?:[ ]+|(?=\n))))
			}xm',
            array($this, '_processListItems_callback'),
            $list_str
        );

        $this->list_level--;

        return $list_str;
    }

    protected function _processListItems_callback($matches)
    {
        $item = $matches[4];
        $leading_line = &$matches[1];
        $leading_space = &$matches[2];
        $marker_space = $matches[3];
        $tailing_blank_line = &$matches[5];

        if ($leading_line || $tailing_blank_line ||
            preg_match('/\n{2,}/', $item)) {
            // Replace marker with the appropriate whitespace indentation
            $item = $leading_space . str_repeat(' ', strlen($marker_space)) . $item;
            $item = $this->runBlockGamut($this->outdent($item) . "\n");
        } else {
            // Recursion for sub-lists:
            $item = $this->doLists($this->outdent($item));
            $item = preg_replace('/\n+$/', '', $item);
            $item = $this->runSpanGamut($item);
        }

        return "<li>" . $item . "</li>\n";
    }

    protected function doCodeBlocks($text)
    {
        //
        //	Process Markdown `<pre><code>` blocks.
        //
        $text = preg_replace_callback(
            '{
				(?:\n\n|\A\n?)
				(	            # $1 = the code block -- one or more lines, starting with a space/tab
				  (?>
					[ ]{' . $this->tab_width . '}  # Lines must start with a tab or a tab-width of spaces
					.*\n+
				  )+
				)
				((?=^[ ]{0,' . $this->tab_width . '}\S)|\Z)	# Lookahead for non-space at line-start, or end of doc
			}xm',
            array($this, '_doCodeBlocks_callback'),
            $text
        );

        return $text;
    }

    protected function _doCodeBlocks_callback($matches)
    {
        $codeblock = $matches[1];

        $codeblock = $this->outdent($codeblock);
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);

        // trim leading newlines and trailing newlines
        $codeblock = preg_replace('/\A\n+|\n+\z/', '', $codeblock);

        $codeblock = "<pre><code>$codeblock\n</code></pre>";

        return "\n\n" . $this->hashBlock($codeblock) . "\n\n";
    }

    protected function makeCodeSpan($code)
    {
        //
        // Create a code span markup for $code. Called from handleSpanToken.
        //
        $code = htmlspecialchars(trim($code), ENT_NOQUOTES);

        return $this->hashPart("<code>$code</code>");
    }

    protected $em_relist = array(
        ''  => '(?:(?<!\*)\*(?!\*)|(?<!_)_(?!_))(?![\.,:;]?\s)',
        '*' => '(?<![\s*])\*(?!\*)',
        '_' => '(?<![\s_])_(?!_)',
    );
    protected $strong_relist = array(
        ''   => '(?:(?<!\*)\*\*(?!\*)|(?<!_)__(?!_))(?![\.,:;]?\s)',
        '**' => '(?<![\s*])\*\*(?!\*)',
        '__' => '(?<![\s_])__(?!_)',
    );
    protected $em_strong_relist = array(
        ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<!_)___(?!_))(?![\.,:;]?\s)',
        '***' => '(?<![\s*])\*\*\*(?!\*)',
        '___' => '(?<![\s_])___(?!_)',
    );
    protected $em_strong_prepared_relist;

    protected function prepareItalicsAndBold()
    {
        //
        // Prepare regular expressions for searching emphasis tokens in any
        // context.
        //
        foreach ($this->em_relist as $em => $em_re) {
            foreach ($this->strong_relist as $strong => $strong_re) {
                // Construct list of allowed token expressions.
                $token_relist = array();
                if (isset($this->em_strong_relist["$em$strong"])) {
                    $token_relist[] = $this->em_strong_relist["$em$strong"];
                }
                $token_relist[] = $em_re;
                $token_relist[] = $strong_re;

                // Construct master expression from list.
                $token_re = '{(' . implode('|', $token_relist) . ')}';
                $this->em_strong_prepared_relist["$em$strong"] = $token_re;
            }
        }
    }

    protected function doItalicsAndBold($text)
    {
        $token_stack = array('');
        $text_stack = array('');
        $em = '';
        $strong = '';
        $tree_char_em = false;

        while (1) {
            //
            // Get prepared regular expression for seraching emphasis tokens
            // in current context.
            //
            $token_re = $this->em_strong_prepared_relist["$em$strong"];

            //
            // Each loop iteration search for the next emphasis token.
            // Each token is then passed to handleSpanToken.
            //
            $parts = preg_split($token_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
            $text_stack[0] .= $parts[0];
            $token = &$parts[1];
            $text = &$parts[2];

            if (empty($token)) {
                // Reached end of text span: empty stack without emitting.
                // any more emphasis.
                while ($token_stack[0]) {
                    $text_stack[1] .= array_shift($token_stack);
                    $text_stack[0] .= array_shift($text_stack);
                }
                break;
            }

            $token_len = strlen($token);
            if ($tree_char_em) {
                // Reached closing marker while inside a three-char emphasis.
                if ($token_len == 3) {
                    // Three-char closing marker, close em and strong.
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong><em>$span</em></strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $em = '';
                    $strong = '';
                } else {
                    // Other closing marker: close one em or strong and
                    // change current token state to match the other
                    $token_stack[0] = str_repeat($token[0], 3 - $token_len);
                    $tag = $token_len == 2 ? "strong" : "em";
                    $span = $text_stack[0];
                    $span = $this->runSpanGamut($span);
                    $span = "<$tag>$span</$tag>";
                    $text_stack[0] = $this->hashPart($span);
                    $$tag = ''; // $$tag stands for $em or $strong
                }
                $tree_char_em = false;
            } elseif ($token_len == 3) {
                if ($em) {
                    // Reached closing marker for both em and strong.
                    // Closing strong marker:
                    for ($i = 0; $i < 2; $i++) {
                        $shifted_token = array_shift($token_stack);
                        $tag = strlen($shifted_token) == 2 ? "strong" : "em";
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<$tag>$span</$tag>";
                        $text_stack[0] .= $this->hashPart($span);
                        $$tag = ''; // $$tag stands for $em or $strong
                    }
                } else {
                    // Reached opening three-char emphasis marker. Push on token
                    // stack; will be handled by the special condition above.
                    $em = $token[0];
                    $strong = "$em$em";
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $tree_char_em = true;
                }
            } elseif ($token_len == 2) {
                if ($strong) {
                    // Unwind any dangling emphasis marker:
                    if (strlen($token_stack[0]) == 1) {
                        $text_stack[1] .= array_shift($token_stack);
                        $text_stack[0] .= array_shift($text_stack);
                    }
                    // Closing strong marker:
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong>$span</strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $strong = '';
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $strong = $token;
                }
            } else {
                // Here $token_len == 1
                if ($em) {
                    if (strlen($token_stack[0]) == 1) {
                        // Closing emphasis marker:
                        array_shift($token_stack);
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<em>$span</em>";
                        $text_stack[0] .= $this->hashPart($span);
                        $em = '';
                    } else {
                        $text_stack[0] .= $token;
                    }
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $em = $token;
                }
            }
        }

        return $text_stack[0];
    }

    protected function doBlockQuotes($text)
    {
        $text = preg_replace_callback(
            '/
			  (								# Wrap whole match in $1
				(?>
				  ^[ ]*>[ ]?			# ">" at the start of a line
					.+\n					# rest of the first line
				  (.+\n)*					# subsequent consecutive lines
				  \n*						# blanks
				)+
			  )
			/xm',
            array($this, '_doBlockQuotes_callback'),
            $text
        );

        return $text;
    }

    protected function _doBlockQuotes_callback($matches)
    {
        $bq = $matches[1];
        // trim one level of quoting - trim whitespace-only lines
        $bq = preg_replace('/^[ ]*>[ ]?|^[ ]+$/m', '', $bq);
        $bq = $this->runBlockGamut($bq);        // recurse

        $bq = preg_replace('/^/m', "  ", $bq);
        // These leading spaces cause problem with <pre> content,
        // so we need to fix that:
        $bq = preg_replace_callback(
            '{(\s*<pre>.+?</pre>)}sx',
            array($this, '_doBlockQuotes_callback2'),
            $bq
        );

        return "\n" . $this->hashBlock("<blockquote>\n$bq\n</blockquote>") . "\n\n";
    }

    protected function _doBlockQuotes_callback2($matches)
    {
        $pre = $matches[1];
        $pre = preg_replace('/^  /m', '', $pre);

        return $pre;
    }

    protected function formParagraphs($text)
    {
        //
        //	Params:
        //		$text - string to process with html <p> tags
        //
        // Strip leading and trailing lines:
        $text = preg_replace('/\A\n+|\n+\z/', '', $text);

        $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

        //
        // Wrap <p> tags and unhashify HTML blocks
        //
        foreach ($grafs as $key => $value) {
            if (!preg_match('/^B\x1A[0-9]+B$/', $value)) {
                // Is a paragraph.
                $value = $this->runSpanGamut($value);
                $value = preg_replace('/^([ ]*)/', "<p>", $value);
                $value .= "</p>";
                $grafs[$key] = $this->unhash($value);
            } else {
                // Is a block.
                // Modify elements of @grafs in-place...
                $graf = $value;
                $block = $this->html_hashes[$graf];
                $graf = $block;
                //				if (preg_match('{
                //					\A
                //					(							# $1 = <div> tag
                //					  <div  \s+
                //					  [^>]*
                //					  \b
                //					  markdown\s*=\s*  ([\'"])	#	$2 = attr quote char
                //					  1
                //					  \2
                //					  [^>]*
                //					  >
                //					)
                //					(							# $3 = contents
                //					.*
                //					)
                //					(</div>)					# $4 = closing tag
                //					\z
                //					}xs', $block, $matches))
                //				{
                //					list(, $div_open, , $div_content, $div_close) = $matches;
//
                //					# We can't call Markdown(), because that resets the hash;
                //					# that initialization code should be pulled into its own sub, though.
                //					$div_content = $this->hashHTMLBlocks($div_content);
//
                //					# Run document gamut methods on the content.
                //					foreach ($this->document_gamut as $method => $priority) {
                //						$div_content = $this->$method($div_content);
                //					}
//
                //					$div_open = preg_replace(
                //						'{\smarkdown\s*=\s*([\'"]).+?\1}', '', $div_open);
//
                //					$graf = $div_open . "\n" . $div_content . "\n" . $div_close;
                //				}
                $grafs[$key] = $graf;
            }
        }

        return implode("\n\n", $grafs);
    }

    protected function encodeAttribute($text)
    {
        //
        // Encode text for a double-quoted HTML attribute. This function
        // is *not* suitable for attributes enclosed in single quotes.
        //
        $text = $this->encodeAmpsAndAngles($text);
        $text = str_replace('"', '&quot;', $text);

        return $text;
    }

    protected function encodeURLAttribute($url, &$text = null)
    {
        //
        // Encode text for a double-quoted HTML attribute containing a URL,
        // applying the URL filter if set. Also generates the textual
        // representation for the URL (removing mailto: or tel:) storing it in $text.
        // This function is *not* suitable for attributes enclosed in single quotes.
        //
        if ($this->url_filter_func) {
            $url = call_user_func($this->url_filter_func, $url);
        }

        if (preg_match('{^mailto:}i', $url)) {
            $url = $this->encodeEntityObfuscatedAttribute($url, $text, 7);
        } elseif (preg_match('{^tel:}i', $url)) {
            $url = $this->encodeAttribute($url);
            $text = substr($url, 4);
        } else {
            $url = $this->encodeAttribute($url);
            $text = $url;
        }

        return $url;
    }

    protected function encodeAmpsAndAngles($text)
    {
        //
        // Smart processing for ampersands and angle brackets that need to
        // be encoded. Valid character entities are left alone unless the
        // no-entities mode is set.
        //
        if ($this->no_entities) {
            $text = str_replace('&', '&amp;', $text);
        } else {
            // Ampersand-encoding based entirely on Nat Irons's Amputator
            // MT plugin: <http://bumppo.net/projects/amputator/>
            $text = preg_replace(
                '/&(?!#?[xX]?(?:[0-9a-fA-F]+|\w+);)/',
                '&amp;',
                $text
            );
        }
        // Encode remaining <'s
        $text = str_replace('<', '&lt;', $text);

        return $text;
    }

    protected function doAutoLinks($text)
    {
        $text = preg_replace_callback(
            '{<((https?|ftp|dict|tel):[^\'">\s]+)>}i',
            array($this, '_doAutoLinks_url_callback'),
            $text
        );

        // Email addresses: <address@domain.foo>
        $text = preg_replace_callback(
            '{
			<
			(?:mailto:)?
			(
				(?:
					[-!#$%&\'*+/=?^_`.{|}~\w\x80-\xFF]+
				|
					".*?"
				)
				\@
				(?:
					[-a-z0-9\x80-\xFF]+(\.[-a-z0-9\x80-\xFF]+)*\.[a-z]+
				|
					\[[\d.a-fA-F:]+\]	# IPv4 & IPv6
				)
			)
			>
			}xi',
            array($this, '_doAutoLinks_email_callback'),
            $text
        );

        return $text;
    }

    protected function _doAutoLinks_url_callback($matches)
    {
        $url = $this->encodeURLAttribute($matches[1], $text);
        $link = "<a href=\"$url\">$text</a>";

        return $this->hashPart($link);
    }

    protected function _doAutoLinks_email_callback($matches)
    {
        $addr = $matches[1];
        $url = $this->encodeURLAttribute("mailto:$addr", $text);
        $link = "<a href=\"$url\">$text</a>";

        return $this->hashPart($link);
    }

    protected function encodeEntityObfuscatedAttribute($text, &$tail = null, $head_length = 0)
    {
        //
        //	Input: some text to obfuscate, e.g. "mailto:foo@example.com"
        //
        //	Output: the same text but with most characters encoded as either a
        //		decimal or hex entity, in the hopes of foiling most address
        //		harvesting spam bots. E.g.:
        //
        //        &#109;&#x61;&#105;&#x6c;&#116;&#x6f;&#58;&#x66;o&#111;
        //        &#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;&#101;&#46;&#x63;&#111;
        //        &#x6d;
        //
        //	Note: the additional output $tail is assigned the same value as the
        //	ouput, minus the number of characters specified by $head_length.
        //
        //	Based by a filter by Matthew Wickline, posted to BBEdit-Talk.
        //   With some optimizations by Milian Wolff. Forced encoding of HTML
        //	attribute special characters by Allan Odgaard.
        //
        if ($text == "") {
            return $tail = "";
        }

        $chars = preg_split('/(?<!^)(?!$)/', $text);
        $seed = (int) abs(crc32($text) / strlen($text)); // Deterministic seed.

        foreach ($chars as $key => $char) {
            $ord = ord($char);
            // Ignore non-ascii chars.
            if ($ord < 128) {
                $r = ($seed * (1 + $key)) % 100; // Pseudo-random function.
                // roughly 10% raw, 45% hex, 45% dec
                // '@' *must* be encoded. I insist.
                // '"' and '>' have to be encoded inside the attribute
                if ($r > 90 && strpos('@"&>', $char) === false) /* do nothing */; elseif ($r < 45) {
                    $chars[$key] = '&#x' . dechex($ord) . ';';
                } else {
                    $chars[$key] = '&#' . $ord . ';';
                }
            }
        }

        $text = implode('', $chars);
        $tail = $head_length ? implode('', array_slice($chars, $head_length)) : $text;

        return $text;
    }

    protected function parseSpan($str)
    {
        //
        // Take the string $str and parse it into tokens, hashing embeded HTML,
        // escaped characters and handling code spans.
        //
        $output = '';

        $span_re = '{
				(
					\\\\' . $this->escape_chars_re . '
				|
					(?<![`\\\\])
					`+						# code span marker
			' . ($this->no_markup ? '' : '
				|
					<!--    .*?     -->		# comment
				|
					<\?.*?\?> | <%.*?%>		# processing instruction
				|
					<[!$]?[-a-zA-Z0-9:_]+	# regular tags
					(?>
						\s
						(?>[^"\'>]+|"[^"]*"|\'[^\']*\')*
					)?
					>
				|
					<[-a-zA-Z0-9:_]+\s*/> # xml-style empty tag
				|
					</[-a-zA-Z0-9:_]+\s*> # closing tag
			') . '
				)
				}xs';

        while (1) {
            //
            // Each loop iteration seach for either the next tag, the next
            // openning code span marker, or the next escaped character.
            // Each token is then passed to handleSpanToken.
            //
            $parts = preg_split($span_re, $str, 2, PREG_SPLIT_DELIM_CAPTURE);

            // Create token from text preceding tag.
            if ($parts[0] != "") {
                $output .= $parts[0];
            }

            // Check if we reach the end.
            if (isset($parts[1])) {
                $output .= $this->handleSpanToken($parts[1], $parts[2]);
                $str = $parts[2];
            } else {
                break;
            }
        }

        return $output;
    }

    protected function handleSpanToken($token, &$str)
    {
        //
        // Handle $token provided by parseSpan by determining its nature and
        // returning the corresponding value that should replace it.
        //
        switch ($token[0]) {
            case "\\":
                return $this->hashPart("&#" . ord($token[1]) . ";");
            case "`":
                // Search for end marker in remaining text.
                if (preg_match(
                    '/^(.*?[^`])' . preg_quote($token) . '(?!`)(.*)$/sm',
                    $str,
                    $matches
                )) {
                    $str = $matches[2];
                    $codespan = $this->makeCodeSpan($matches[1]);

                    return $this->hashPart($codespan);
                }

                return $token; // return as text since no ending marker found.
            default:
                return $this->hashPart($token);
        }
    }

    protected function outdent($text)
    {
        //
        // Remove one level of line-leading tabs or spaces
        //
        return preg_replace('/^(\t|[ ]{1,' . $this->tab_width . '})/m', '', $text);
    }

    // String length function for detab. `_initDetab` will create a function to
    // hanlde UTF-8 if the default function does not exist.
    protected $utf8_strlen = 'mb_strlen';

    protected function detab($text)
    {
        //
        // Replace tabs with the appropriate amount of space.
        //
        // For each line we separate the line in blocks delemited by
        // tab characters. Then we reconstruct every line by adding the
        // appropriate number of space between each blocks.

        $text = preg_replace_callback(
            '/^.*\t.*$/m',
            array($this, '_detab_callback'),
            $text
        );

        return $text;
    }

    protected function _detab_callback($matches)
    {
        $line = $matches[0];
        $strlen = $this->utf8_strlen; // strlen function for UTF-8.

        // Split in blocks.
        $blocks = explode("\t", $line);
        // Add each blocks to the line.
        $line = $blocks[0];
        unset($blocks[0]); // Do not add first block twice.
        foreach ($blocks as $block) {
            // Calculate amount of space, insert spaces, insert block.
            $amount = $this->tab_width -
                $strlen($line, 'UTF-8') % $this->tab_width;
            $line .= str_repeat(" ", $amount) . $block;
        }

        return $line;
    }

    protected function _initDetab()
    {
        //
        // Check for the availability of the function in the `utf8_strlen` property
        // (initially `mb_strlen`). If the function is not available, create a
        // function that will loosely count the number of UTF-8 characters with a
        // regular expression.
        //
        if (function_exists($this->utf8_strlen)) {
            return;
        }
        $this->utf8_strlen = create_function('$text', 'return preg_match_all(
			"/[\\\\x00-\\\\xBF]|[\\\\xC0-\\\\xFF][\\\\x80-\\\\xBF]*/", 
			$text, $m);');
    }

    protected function unhash($text)
    {
        //
        // Swap back in all the tags hashed by _HashHTMLBlocks.
        //
        return preg_replace_callback(
            '/(.)\x1A[0-9]+\1/',
            array($this, '_unhash_callback'),
            $text
        );
    }

    protected function _unhash_callback($matches)
    {
        return $this->html_hashes[$matches[0]];
    }
}

//
// Temporary Markdown Extra Parser Implementation Class
//
// NOTE: DON'T USE THIS CLASS
// Currently the implementation of of Extra resides here in this temporary class.
// This makes it easier to propagate the changes between the three different
// packaging styles of PHP Markdown. When this issue is resolved, this
// MarkdownExtra_TmpImpl class here will disappear and \Michelf\MarkdownExtra
// will contain the code. So please use \Michelf\MarkdownExtra and ignore this
// one.
//

abstract class _MarkdownExtra_TmpImpl extends Markdown
{
    //## Configuration Variables ###

    // Prefix for footnote ids.
    public $fn_id_prefix = "";

    // Optional title attribute for footnote links and backlinks.
    public $fn_link_title = "";
    public $fn_backlink_title = "";

    // Optional class attribute for footnote links and backlinks.
    public $fn_link_class = "footnote-ref";
    public $fn_backlink_class = "footnote-backref";

    // Class name for table cell alignment (%% replaced left/center/right)
    // For instance: 'go-%%' becomes 'go-left' or 'go-right' or 'go-center'
    // If empty, the align attribute is used instead of a class name.
    public $table_align_class_tmpl = '';

    // Optional class prefix for fenced code block.
    public $code_class_prefix = "";
    // Class attribute for code blocks goes on the `code` tag;
    // setting this to true will put attributes on the `pre` tag instead.
    public $code_attr_on_pre = false;

    // Predefined abbreviations.
    public $predef_abbr = array();

    //## Parser Implementation ###

    public function __construct()
    {
        //
        // Constructor function. Initialize the parser object.
        //
        // Add extra escapable characters before parent constructor
        // initialize the table.
        $this->escape_chars .= ':|';

        // Insert extra document, block, and span transformations.
        // Parent constructor will do the sorting.
        $this->document_gamut += array(
            "doFencedCodeBlocks" => 5,
            "stripFootnotes"     => 15,
            "stripAbbreviations" => 25,
            "appendFootnotes"    => 50,
        );
        $this->block_gamut += array(
            "doFencedCodeBlocks" => 5,
            "doTables"           => 15,
            "doDefLists"         => 45,
        );
        $this->span_gamut += array(
            "doFootnotes"        => 5,
            "doAbbreviations"    => 70,
        );

        parent::__construct();
    }

    // Extra variables used during extra transformations.
    protected $footnotes = array();
    protected $footnotes_ordered = array();
    protected $footnotes_ref_count = array();
    protected $footnotes_numbers = array();
    protected $abbr_desciptions = array();
    protected $abbr_word_re = '';

    // Give the current footnote number.
    protected $footnote_counter = 1;

    protected function setup()
    {
        //
        // Setting up Extra-specific variables.
        //
        parent::setup();

        $this->footnotes = array();
        $this->footnotes_ordered = array();
        $this->footnotes_ref_count = array();
        $this->footnotes_numbers = array();
        $this->abbr_desciptions = array();
        $this->abbr_word_re = '';
        $this->footnote_counter = 1;

        foreach ($this->predef_abbr as $abbr_word => $abbr_desc) {
            if ($this->abbr_word_re) {
                $this->abbr_word_re .= '|';
            }
            $this->abbr_word_re .= preg_quote($abbr_word);
            $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);
        }
    }

    protected function teardown()
    {
        //
        // Clearing Extra-specific variables.
        //
        $this->footnotes = array();
        $this->footnotes_ordered = array();
        $this->footnotes_ref_count = array();
        $this->footnotes_numbers = array();
        $this->abbr_desciptions = array();
        $this->abbr_word_re = '';

        parent::teardown();
    }

    //## Extra Attribute Parser ###

    // Expression to use to catch attributes (includes the braces)
    protected $id_class_attr_catch_re = '\{((?:[ ]*[#.a-z][-_:a-zA-Z0-9=]+){1,})[ ]*\}';
    // Expression to use when parsing in a context when no capture is desired
    protected $id_class_attr_nocatch_re = '\{(?:[ ]*[#.a-z][-_:a-zA-Z0-9=]+){1,}[ ]*\}';

    protected function doExtraAttributes($tag_name, $attr)
    {
        //
        // Parse attributes caught by the $this->id_class_attr_catch_re expression
        // and return the HTML-formatted list of attributes.
        //
        // Currently supported attributes are .class and #id.
        //
        if (empty($attr)) {
            return "";
        }

        // Split on components
        preg_match_all('/[#.a-z][-_:a-zA-Z0-9=]+/', $attr, $matches);
        $elements = $matches[0];

        // handle classes and ids (only first id taken into account)
        $classes = array();
        $attributes = array();
        $id = false;
        foreach ($elements as $element) {
            if ($element[0] == '.') {
                $classes[] = substr($element, 1);
            } elseif ($element[0] == '#') {
                if ($id === false) {
                    $id = substr($element, 1);
                }
            } elseif (strpos($element, '=') > 0) {
                $parts = explode('=', $element, 2);
                $attributes[] = $parts[0] . '="' . $parts[1] . '"';
            }
        }

        // compose attributes as string
        $attr_str = "";
        if (!empty($id)) {
            $attr_str .= ' id="' . $id . '"';
        }
        if (!empty($classes)) {
            $attr_str .= ' class="' . implode(" ", $classes) . '"';
        }
        if (!$this->no_markup && !empty($attributes)) {
            $attr_str .= ' ' . implode(" ", $attributes);
        }

        return $attr_str;
    }

    protected function stripLinkDefinitions($text)
    {
        //
        // Strips link definitions from text, stores the URLs and titles in
        // hash references.
        //
        $less_than_tab = $this->tab_width - 1;

        // Link defs are in the form: ^[id]: url "optional title"
        $text = preg_replace_callback(
            '{
							^[ ]{0,' . $less_than_tab . '}\[(.+)\][ ]?:	# id = $1
							  [ ]*
							  \n?				# maybe *one* newline
							  [ ]*
							(?:
							  <(.+?)>			# url = $2
							|
							  (\S+?)			# url = $3
							)
							  [ ]*
							  \n?				# maybe one newline
							  [ ]*
							(?:
								(?<=\s)			# lookbehind for whitespace
								["(]
								(.*?)			# title = $4
								[")]
								[ ]*
							)?	# title is optional
					(?:[ ]* ' . $this->id_class_attr_catch_re . ' )?  # $5 = extra id & class attr
							(?:\n+|\Z)
			}xm',
            array($this, '_stripLinkDefinitions_callback'),
            $text
        );

        return $text;
    }

    protected function _stripLinkDefinitions_callback($matches)
    {
        $link_id = strtolower($matches[1]);
        $url = $matches[2] == '' ? $matches[3] : $matches[2];
        $this->urls[$link_id] = $url;
        $this->titles[$link_id] = &$matches[4];
        $this->ref_attr[$link_id] = $this->doExtraAttributes("", $dummy = &$matches[5]);

        return ''; // String that will replace the block
    }

    //## HTML Block Parser ###

    // Tags that are always treated as block tags:
    protected $block_tags_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|form|fieldset|iframe|hr|legend|article|section|nav|aside|hgroup|header|footer|figcaption|figure';

    // Tags treated as block tags only if the opening tag is alone on its line:
    protected $context_block_tags_re = 'script|noscript|style|ins|del|iframe|object|source|track|param|math|svg|canvas|audio|video';

    // Tags where markdown="1" default to span mode:
    protected $contain_span_tags_re = 'p|h[1-6]|li|dd|dt|td|th|legend|address';

    // Tags which must not have their contents modified, no matter where
    // they appear:
    protected $clean_tags_re = 'script|style|math|svg';

    // Tags that do not need to be closed.
    protected $auto_close_tags_re = 'hr|img|param|source|track';

    protected function hashHTMLBlocks($text)
    {
        //
        // Hashify HTML Blocks and "clean tags".
        //
        // We only want to do this for block-level HTML tags, such as headers,
        // lists, and tables. That's because we still want to wrap <p>s around
        // "paragraphs" that are wrapped in non-block-level tags, such as anchors,
        // phrase emphasis, and spans. The list of tags we're looking for is
        // hard-coded.
        //
        // This works by calling _HashHTMLBlocks_InMarkdown, which then calls
        // _HashHTMLBlocks_InHTML when it encounter block tags. When the markdown="1"
        // attribute is found within a tag, _HashHTMLBlocks_InHTML calls back
        //  _HashHTMLBlocks_InMarkdown to handle the Markdown syntax within the tag.
        // These two functions are calling each other. It's recursive!
        //
        if ($this->no_markup) {
            return $text;
        }

        //
        // Call the HTML-in-Markdown hasher.
        //
        list($text) = $this->_hashHTMLBlocks_inMarkdown($text);

        return $text;
    }

    protected function _hashHTMLBlocks_inMarkdown(
        $text,
        $indent = 0,
        $enclosing_tag_re = '',
        $span = false
    ) {
        //
        // Parse markdown text, calling _HashHTMLBlocks_InHTML for block tags.
        //
        // *   $indent is the number of space to be ignored when checking for code
        //     blocks. This is important because if we don't take the indent into
        //     account, something like this (which looks right) won't work as expected:
        //
        //     <div>
        //         <div markdown="1">
        //         Hello World.  <-- Is this a Markdown code block or text?
        //         </div>  <-- Is this a Markdown code block or a real tag?
        //     <div>
        //
        //     If you don't like this, just don't indent the tag on which
        //     you apply the markdown="1" attribute.
        //
        // *   If $enclosing_tag_re is not empty, stops at the first unmatched closing
        //     tag with that name. Nested tags supported.
        //
        // *   If $span is true, text inside must treated as span. So any double
        //     newline will be replaced by a single newline so that it does not create
        //     paragraphs.
        //
        // Returns an array of that form: ( processed text , remaining text )
        //
        if ($text === '') {
            return array('', '');
        }

        // Regex to check for the presense of newlines around a block tag.
        $newline_before_re = '/(?:^\n?|\n\n)*$/';
        $newline_after_re =
            '{
				^						# Start of text following the tag.
				(?>[ ]*<!--.*?-->)?		# Optional comment.
				[ ]*\n					# Must be followed by newline.
			}xs';

        // Regex to match any tag.
        $block_tag_re =
            '{
				(					# $2: Capture whole tag.
					</?					# Any opening or closing tag.
						(?>				# Tag name.
							' . $this->block_tags_re . '			|
							' . $this->context_block_tags_re . '	|
							' . $this->clean_tags_re . '        	|
							(?!\s)' . $enclosing_tag_re . '
						)
						(?:
							(?=[\s"\'/a-zA-Z0-9])	# Allowed characters after tag name.
							(?>
								".*?"		|	# Double quotes (can contain `>`)
								\'.*?\'   	|	# Single quotes (can contain `>`)
								.+?				# Anything but quotes and `>`.
							)*?
						)?
					>					# End of tag.
				|
					<!--    .*?     -->	# HTML Comment
				|
					<\?.*?\?> | <%.*?%>	# Processing instruction
				|
					<!\[CDATA\[.*?\]\]>	# CData Block
				' . (!$span ? ' # If not in span.
				|
					# Indented code block
					(?: ^[ ]*\n | ^ | \n[ ]*\n )
					[ ]{' . ($indent + 4) . '}[^\n]* \n
					(?>
						(?: [ ]{' . ($indent + 4) . '}[^\n]* | [ ]* ) \n
					)*
				|
					# Fenced code block marker
					(?<= ^ | \n )
					[ ]{0,' . ($indent + 3) . '}(?:~{3,}|`{3,})
									[ ]*
					(?:
					\.?[-_:a-zA-Z0-9]+ # standalone class name
					|
						' . $this->id_class_attr_nocatch_re . ' # extra attributes
					)?
					[ ]*
					(?= \n )
				' : '') . ' # End (if not is span).
				|
					# Code span marker
					# Note, this regex needs to go after backtick fenced
					# code blocks but it should also be kept outside of the
					# "if not in span" condition adding backticks to the parser
					`+
				)
			}xs';

        $depth = 0;        // Current depth inside the tag tree.
        $parsed = "";    // Parsed text that will be returned.

        //
        // Loop through every tag until we find the closing tag of the parent
        // or loop until reaching the end of text if no parent tag specified.
        //
        do {
            //
            // Split the text using the first $tag_match pattern found.
            // Text before  pattern will be first in the array, text after
            // pattern will be at the end, and between will be any catches made
            // by the pattern.
            //
            $parts = preg_split(
                $block_tag_re,
                $text,
                2,
                PREG_SPLIT_DELIM_CAPTURE
            );

            // If in Markdown span mode, add a empty-string span-level hash
            // after each newline to prevent triggering any block element.
            if ($span) {
                $void = $this->hashPart("", ':');
                $newline = "$void\n";
                $parts[0] = $void . str_replace("\n", $newline, $parts[0]) . $void;
            }

            $parsed .= $parts[0]; // Text before current tag.

            // If end of $text has been reached. Stop loop.
            if (count($parts) < 3) {
                $text = "";
                break;
            }

            $tag = $parts[1]; // Tag to handle.
            $text = $parts[2]; // Remaining text after current tag.
            $tag_re = preg_quote($tag); // For use in a regular expression.

            //
            // Check for: Fenced code block marker.
            // Note: need to recheck the whole tag to disambiguate backtick
            // fences from code spans
            //
            if (preg_match('{^\n?([ ]{0,' . ($indent + 3) . '})(~{3,}|`{3,})[ ]*(?:\.?[-_:a-zA-Z0-9]+|' . $this->id_class_attr_nocatch_re . ')?[ ]*\n?$}', $tag, $capture)) {
                // Fenced code block marker: find matching end marker.
                $fence_indent = strlen($capture[1]); // use captured indent in re
                $fence_re = $capture[2]; // use captured fence in re
                if (preg_match(
                    '{^(?>.*\n)*?[ ]{' . ($fence_indent) . '}' . $fence_re . '[ ]*(?:\n|$)}',
                    $text,
                    $matches
                )) {
                    // End marker found: pass text unchanged until marker.
                    $parsed .= $tag . $matches[0];
                    $text = substr($text, strlen($matches[0]));
                } else {
                    // No end marker: just skip it.
                    $parsed .= $tag;
                }
            }
            //
            // Check for: Indented code block.
            //
            elseif ($tag[0] == "\n" || $tag[0] == " ") {
                // Indented code block: pass it unchanged, will be handled
                // later.
                $parsed .= $tag;
            }
            //
            // Check for: Code span marker
            // Note: need to check this after backtick fenced code blocks
            //
            elseif ($tag[0] == "`") {
                // Find corresponding end marker.
                $tag_re = preg_quote($tag);
                if (preg_match(
                    '{^(?>.+?|\n(?!\n))*?(?<!`)' . $tag_re . '(?!`)}',
                    $text,
                    $matches
                )) {
                    // End marker found: pass text unchanged until marker.
                    $parsed .= $tag . $matches[0];
                    $text = substr($text, strlen($matches[0]));
                } else {
                    // Unmatched marker: just skip it.
                    $parsed .= $tag;
                }
            }
            //
            // Check for: Opening Block level tag or
            //            Opening Context Block tag (like ins and del)
            //               used as a block tag (tag is alone on it's line).
            //
            elseif (preg_match('{^<(?:' . $this->block_tags_re . ')\b}', $tag) ||
                (preg_match('{^<(?:' . $this->context_block_tags_re . ')\b}', $tag) &&
                    preg_match($newline_before_re, $parsed) &&
                    preg_match($newline_after_re, $text))
                ) {
                // Need to parse tag and following text using the HTML parser.
                list($block_text, $text) =
                    $this->_hashHTMLBlocks_inHTML($tag . $text, "hashBlock", true);

                // Make sure it stays outside of any paragraph by adding newlines.
                $parsed .= "\n\n$block_text\n\n";
            }
            //
            // Check for: Clean tag (like script, math)
            //            HTML Comments, processing instructions.
            //
            elseif (preg_match('{^<(?:' . $this->clean_tags_re . ')\b}', $tag) ||
                $tag[1] == '!' || $tag[1] == '?') {
                // Need to parse tag and following text using the HTML parser.
                // (don't check for markdown attribute)
                list($block_text, $text) =
                    $this->_hashHTMLBlocks_inHTML($tag . $text, "hashClean", false);

                $parsed .= $block_text;
            }
            //
            // Check for: Tag with same name as enclosing tag.
            //
            elseif ($enclosing_tag_re !== '' &&
                // Same name as enclosing tag.
                preg_match('{^</?(?:' . $enclosing_tag_re . ')\b}', $tag)) {
                //
                // Increase/decrease nested tag count.
                //
                if ($tag[1] == '/') {
                    $depth--;
                } elseif ($tag[strlen($tag) - 2] != '/') {
                    $depth++;
                }

                if ($depth < 0) {
                    //
                    // Going out of parent element. Clean up and break so we
                    // return to the calling function.
                    //
                    $text = $tag . $text;
                    break;
                }

                $parsed .= $tag;
            } else {
                $parsed .= $tag;
            }
        } while ($depth >= 0);

        return array($parsed, $text);
    }

    protected function _hashHTMLBlocks_inHTML($text, $hash_method, $md_attr)
    {
        //
        // Parse HTML, calling _HashHTMLBlocks_InMarkdown for block tags.
        //
        // *   Calls $hash_method to convert any blocks.
        // *   Stops when the first opening tag closes.
        // *   $md_attr indicate if the use of the `markdown="1"` attribute is allowed.
        //     (it is not inside clean tags)
        //
        // Returns an array of that form: ( processed text , remaining text )
        //
        if ($text === '') {
            return array('', '');
        }

        // Regex to match `markdown` attribute inside of a tag.
        $markdown_attr_re = '
			{
				\s*			# Eat whitespace before the `markdown` attribute
				markdown
				\s*=\s*
				(?>
					(["\'])		# $1: quote delimiter		
					(.*?)		# $2: attribute value
					\1			# matching delimiter	
				|
					([^\s>]*)	# $3: unquoted attribute value
				)
				()				# $4: make $3 always defined (avoid warnings)
			}xs';

        // Regex to match any tag.
        $tag_re = '{
				(					# $2: Capture whole tag.
					</?					# Any opening or closing tag.
						[\w:$]+			# Tag name.
						(?:
							(?=[\s"\'/a-zA-Z0-9])	# Allowed characters after tag name.
							(?>
								".*?"		|	# Double quotes (can contain `>`)
								\'.*?\'   	|	# Single quotes (can contain `>`)
								.+?				# Anything but quotes and `>`.
							)*?
						)?
					>					# End of tag.
				|
					<!--    .*?     -->	# HTML Comment
				|
					<\?.*?\?> | <%.*?%>	# Processing instruction
				|
					<!\[CDATA\[.*?\]\]>	# CData Block
				)
			}xs';

        $original_text = $text;        // Save original text in case of faliure.

        $depth = 0;    // Current depth inside the tag tree.
        $block_text = "";    // Temporary text holder for current text.
        $parsed = "";    // Parsed text that will be returned.

        //
        // Get the name of the starting tag.
        // (This pattern makes $base_tag_name_re safe without quoting.)
        //
        if (preg_match('/^<([\w:$]*)\b/', $text, $matches)) {
            $base_tag_name_re = $matches[1];
        }

        //
        // Loop through every tag until we find the corresponding closing tag.
        //
        do {
            //
            // Split the text using the first $tag_match pattern found.
            // Text before  pattern will be first in the array, text after
            // pattern will be at the end, and between will be any catches made
            // by the pattern.
            //
            $parts = preg_split($tag_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);

            if (count($parts) < 3) {
                //
                // End of $text reached with unbalenced tag(s).
                // In that case, we return original text unchanged and pass the
                // first character as filtered to prevent an infinite loop in the
                // parent function.
                //
                return array($original_text[0], substr($original_text, 1));
            }

            $block_text .= $parts[0]; // Text before current tag.
            $tag = $parts[1]; // Tag to handle.
            $text = $parts[2]; // Remaining text after current tag.

            //
            // Check for: Auto-close tag (like <hr/>)
            //			 Comments and Processing Instructions.
            //
            if (preg_match('{^</?(?:' . $this->auto_close_tags_re . ')\b}', $tag) ||
                $tag[1] == '!' || $tag[1] == '?') {
                // Just add the tag to the block as if it was text.
                $block_text .= $tag;
            } else {
                //
                // Increase/decrease nested tag count. Only do so if
                // the tag's name match base tag's.
                //
                if (preg_match('{^</?' . $base_tag_name_re . '\b}', $tag)) {
                    if ($tag[1] == '/') {
                        $depth--;
                    } elseif ($tag[strlen($tag) - 2] != '/') {
                        $depth++;
                    }
                }

                //
                // Check for `markdown="1"` attribute and handle it.
                //
                if ($md_attr &&
                    preg_match($markdown_attr_re, $tag, $attr_m) &&
                    preg_match('/^1|block|span$/', $attr_m[2] . $attr_m[3])) {
                    // Remove `markdown` attribute from opening tag.
                    $tag = preg_replace($markdown_attr_re, '', $tag);

                    // Check if text inside this tag must be parsed in span mode.
                    $this->mode = $attr_m[2] . $attr_m[3];
                    $span_mode = $this->mode == 'span' || $this->mode != 'block' &&
                        preg_match('{^<(?:' . $this->contain_span_tags_re . ')\b}', $tag);

                    // Calculate indent before tag.
                    if (preg_match('/(?:^|\n)( *?)(?! ).*?$/', $block_text, $matches)) {
                        $strlen = $this->utf8_strlen;
                        $indent = $strlen($matches[1], 'UTF-8');
                    } else {
                        $indent = 0;
                    }

                    // End preceding block with this tag.
                    $block_text .= $tag;
                    $parsed .= $this->$hash_method($block_text);

                    // Get enclosing tag name for the ParseMarkdown function.
                    // (This pattern makes $tag_name_re safe without quoting.)
                    preg_match('/^<([\w:$]*)\b/', $tag, $matches);
                    $tag_name_re = $matches[1];

                    // Parse the content using the HTML-in-Markdown parser.
                    list($block_text, $text)
                        = $this->_hashHTMLBlocks_inMarkdown(
                            $text,
                            $indent,
                            $tag_name_re,
                            $span_mode
                        );

                    // Outdent markdown text.
                    if ($indent > 0) {
                        $block_text = preg_replace(
                            "/^[ ]{1,$indent}/m",
                            "",
                            $block_text
                        );
                    }

                    // Append tag content to parsed text.
                    if (!$span_mode) {
                        $parsed .= "\n\n$block_text\n\n";
                    } else {
                        $parsed .= "$block_text";
                    }

                    // Start over with a new block.
                    $block_text = "";
                } else {
                    $block_text .= $tag;
                }
            }
        } while ($depth > 0);

        //
        // Hash last block text that wasn't processed inside the loop.
        //
        $parsed .= $this->$hash_method($block_text);

        return array($parsed, $text);
    }

    protected function hashClean($text)
    {
        //
        // Called whenever a tag must be hashed when a function inserts a "clean" tag
        // in $text, it passes through this function and is automaticaly escaped,
        // blocking invalid nested overlap.
        //
        return $this->hashPart($text, 'C');
    }

    protected function doAnchors($text)
    {
        //
        // Turn Markdown link shortcuts into XHTML <a> tags.
        //
        if ($this->in_anchor) {
            return $text;
        }
        $this->in_anchor = true;

        //
        // First, handle reference-style links: [link text] [id]
        //
        $text = preg_replace_callback(
            '{
			(					# wrap whole match in $1
			  \[
				(' . $this->nested_brackets_re . ')	# link text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'),
            $text
        );

        //
        // Next, inline-style links: [link text](url "optional title")
        //
        $text = preg_replace_callback(
            '{
			(				# wrap whole match in $1
			  \[
				(' . $this->nested_brackets_re . ')	# link text = $2
			  \]
			  \(			# literal paren
				[ \n]*
				(?:
					<(.+?)>	# href = $3
				|
					(' . $this->nested_url_parenthesis_re . ')	# href = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# Title = $7
				  \6		# matching quote
				  [ \n]*	# ignore any spaces/tabs between closing quote and )
				)?			# title is optional
			  \)
			  (?:[ ]? ' . $this->id_class_attr_catch_re . ' )?	 # $8 = id/class attributes
			)
			}xs',
            array($this, '_doAnchors_inline_callback'),
            $text
        );

        //
        // Last, handle reference-style shortcuts: [link text]
        // These must come last in case you've also got [link text][1]
        // or [link text](/foo)
        //
        $text = preg_replace_callback(
            '{
			(					# wrap whole match in $1
			  \[
				([^\[\]]+)		# link text = $2; can\'t contain [ or ]
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'),
            $text
        );

        $this->in_anchor = false;

        return $text;
    }

    protected function _doAnchors_reference_callback($matches)
    {
        $whole_match = $matches[1];
        $link_text = $matches[2];
        $link_id = &$matches[3];

        if ($link_id == "") {
            // for shortcut links like [this][] or [this].
            $link_id = $link_text;
        }

        // lower-case and turn embedded newlines into spaces
        $link_id = strtolower($link_id);
        $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

        if (isset($this->urls[$link_id])) {
            $url = $this->urls[$link_id];
            $url = $this->encodeURLAttribute($url);

            $result = "<a href=\"$url\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .= " title=\"$title\"";
            }
            if (isset($this->ref_attr[$link_id])) {
                $result .= $this->ref_attr[$link_id];
            }

            $link_text = $this->runSpanGamut($link_text);
            $result .= ">$link_text</a>";
            $result = $this->hashPart($result);
        } else {
            $result = $whole_match;
        }

        return $result;
    }

    protected function _doAnchors_inline_callback($matches)
    {
        $whole_match = $matches[1];
        $link_text = $this->runSpanGamut($matches[2]);
        $url = $matches[3] == '' ? $matches[4] : $matches[3];
        $title = &$matches[7];
        $attr = $this->doExtraAttributes("a", $dummy = &$matches[8]);

        // if the URL was of the form <s p a c e s> it got caught by the HTML
        // tag parser and hashed. Need to reverse the process before using the URL.
        $unhashed = $this->unhash($url);
        if ($unhashed != $url) {
            $url = preg_replace('/^<(.*)>$/', '\1', $unhashed);
        }

        $url = $this->encodeURLAttribute($url);

        $result = "<a href=\"$url\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .= " title=\"$title\"";
        }
        $result .= $attr;

        $link_text = $this->runSpanGamut($link_text);
        $result .= ">$link_text</a>";

        return $this->hashPart($result);
    }

    protected function doImages($text)
    {
        //
        // Turn Markdown image shortcuts into <img> tags.
        //
        //
        // First, handle reference-style labeled images: ![alt text][id]
        //
        $text = preg_replace_callback(
            '{
			(				# wrap whole match in $1
			  !\[
				(' . $this->nested_brackets_re . ')		# alt text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]

			)
			}xs',
            array($this, '_doImages_reference_callback'),
            $text
        );

        //
        // Next, handle inline images:  ![alt text](url "optional title")
        // Don't forget: encode * and _
        //
        $text = preg_replace_callback(
            '{
			(				# wrap whole match in $1
			  !\[
				(' . $this->nested_brackets_re . ')		# alt text = $2
			  \]
			  \s?			# One optional whitespace character
			  \(			# literal paren
				[ \n]*
				(?:
					<(\S*)>	# src url = $3
				|
					(' . $this->nested_url_parenthesis_re . ')	# src url = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# title = $7
				  \6		# matching quote
				  [ \n]*
				)?			# title is optional
			  \)
			  (?:[ ]? ' . $this->id_class_attr_catch_re . ' )?	 # $8 = id/class attributes
			)
			}xs',
            array($this, '_doImages_inline_callback'),
            $text
        );

        return $text;
    }

    protected function _doImages_reference_callback($matches)
    {
        $whole_match = $matches[1];
        $alt_text = $matches[2];
        $link_id = strtolower($matches[3]);

        if ($link_id == "") {
            $link_id = strtolower($alt_text); // for shortcut links like ![this][].
        }

        $alt_text = $this->encodeAttribute($alt_text);
        if (isset($this->urls[$link_id])) {
            $url = $this->encodeURLAttribute($this->urls[$link_id]);
            $result = "<img src=\"$url\" alt=\"$alt_text\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .= " title=\"$title\"";
            }
            if (isset($this->ref_attr[$link_id])) {
                $result .= $this->ref_attr[$link_id];
            }
            $result .= $this->empty_element_suffix;
            $result = $this->hashPart($result);
        } else {
            // If there's no such link ID, leave intact:
            $result = $whole_match;
        }

        return $result;
    }

    protected function _doImages_inline_callback($matches)
    {
        $whole_match = $matches[1];
        $alt_text = $matches[2];
        $url = $matches[3] == '' ? $matches[4] : $matches[3];
        $title = &$matches[7];
        $attr = $this->doExtraAttributes("img", $dummy = &$matches[8]);

        $alt_text = $this->encodeAttribute($alt_text);
        $url = $this->encodeURLAttribute($url);
        $result = "<img src=\"$url\" alt=\"$alt_text\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .= " title=\"$title\""; // $title already quoted
        }
        $result .= $attr;
        $result .= $this->empty_element_suffix;

        return $this->hashPart($result);
    }

    protected function doHeaders($text)
    {
        //
        // Redefined to add id and class attribute support.
        //
        // Setext-style headers:
        //	  Header 1  {#header1}
        //	  ========
        //
        //	  Header 2  {#header2 .class1 .class2}
        //	  --------
        //
        $text = preg_replace_callback(
            '{
				(^.+?)								# $1: Header text
				(?:[ ]+ ' . $this->id_class_attr_catch_re . ' )?	 # $3 = id/class attributes
				[ ]*\n(=+|-+)[ ]*\n+				# $3: Header footer
			}mx',
            array($this, '_doHeaders_callback_setext'),
            $text
        );

        // atx-style headers:
        //	# Header 1        {#header1}
        //	## Header 2       {#header2}
        //	## Header 2 with closing hashes ##  {#header3.class1.class2}
        //	...
        //	###### Header 6   {.class2}
        //
        $text = preg_replace_callback(
            '{
				^(\#{1,6})	# $1 = string of #\'s
				[ ]*
				(.+?)		# $2 = Header text
				[ ]*
				\#*			# optional closing #\'s (not counted)
				(?:[ ]+ ' . $this->id_class_attr_catch_re . ' )?	 # $3 = id/class attributes
				[ ]*
				\n+
			}xm',
            array($this, '_doHeaders_callback_atx'),
            $text
        );

        return $text;
    }

    protected function _doHeaders_callback_setext($matches)
    {
        if ($matches[3] == '-' && preg_match('{^- }', $matches[1])) {
            return $matches[0];
        }
        $level = $matches[3][0] == '=' ? 1 : 2;
        $attr = $this->doExtraAttributes("h$level", $dummy = &$matches[2]);
        $block = "<h$level$attr>" . $this->runSpanGamut($matches[1]) . "</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }

    protected function _doHeaders_callback_atx($matches)
    {
        $level = strlen($matches[1]);
        $attr = $this->doExtraAttributes("h$level", $dummy = &$matches[3]);
        $block = "<h$level$attr>" . $this->runSpanGamut($matches[2]) . "</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }

    protected function doTables($text)
    {
        //
        // Form HTML tables.
        //
        $less_than_tab = $this->tab_width - 1;
        //
        // Find tables with leading pipe.
        //
        //	| Header 1 | Header 2
        //	| -------- | --------
        //	| Cell 1   | Cell 2
        //	| Cell 3   | Cell 4
        //
        $text = preg_replace_callback(
            '
			{
				^							# Start of a line
				[ ]{0,' . $less_than_tab . '}	# Allowed whitespace.
				[|]							# Optional leading pipe (present)
				(.+) \n						# $1: Header row (at least one pipe)
				
				[ ]{0,' . $less_than_tab . '}	# Allowed whitespace.
				[|] ([ ]*[-:]+[-| :]*) \n	# $2: Header underline
				
				(							# $3: Cells
					(?>
						[ ]*				# Allowed whitespace.
						[|] .* \n			# Row content.
					)*
				)
				(?=\n|\Z)					# Stop at final double newline.
			}xm',
            array($this, '_doTable_leadingPipe_callback'),
            $text
        );

        //
        // Find tables without leading pipe.
        //
        //	Header 1 | Header 2
        //	-------- | --------
        //	Cell 1   | Cell 2
        //	Cell 3   | Cell 4
        //
        $text = preg_replace_callback(
            '
			{
				^							# Start of a line
				[ ]{0,' . $less_than_tab . '}	# Allowed whitespace.
				(\S.*[|].*) \n				# $1: Header row (at least one pipe)
				
				[ ]{0,' . $less_than_tab . '}	# Allowed whitespace.
				([-:]+[ ]*[|][-| :]*) \n	# $2: Header underline
				
				(							# $3: Cells
					(?>
						.* [|] .* \n		# Row content
					)*
				)
				(?=\n|\Z)					# Stop at final double newline.
			}xm',
            array($this, '_DoTable_callback'),
            $text
        );

        return $text;
    }

    protected function _doTable_leadingPipe_callback($matches)
    {
        $head = $matches[1];
        $underline = $matches[2];
        $content = $matches[3];

        // Remove leading pipe for each row.
        $content = preg_replace('/^ *[|]/m', '', $content);

        return $this->_doTable_callback(array($matches[0], $head, $underline, $content));
    }

    protected function _doTable_makeAlignAttr($alignname)
    {
        if (empty($this->table_align_class_tmpl)) {
            return " align=\"$alignname\"";
        }

        $classname = str_replace('%%', $alignname, $this->table_align_class_tmpl);

        return " class=\"$classname\"";
    }

    protected function _doTable_callback($matches)
    {
        $head = $matches[1];
        $underline = $matches[2];
        $content = $matches[3];

        // Remove any tailing pipes for each line.
        $head = preg_replace('/[|] *$/m', '', $head);
        $underline = preg_replace('/[|] *$/m', '', $underline);
        $content = preg_replace('/[|] *$/m', '', $content);

        // Reading alignement from header underline.
        $separators = preg_split('/ *[|] */', $underline);
        foreach ($separators as $n => $s) {
            if (preg_match('/^ *-+: *$/', $s)) {
                $attr[$n] = $this->_doTable_makeAlignAttr('right');
            } elseif (preg_match('/^ *:-+: *$/', $s)) {
                $attr[$n] = $this->_doTable_makeAlignAttr('center');
            } elseif (preg_match('/^ *:-+ *$/', $s)) {
                $attr[$n] = $this->_doTable_makeAlignAttr('left');
            } else {
                $attr[$n] = '';
            }
        }

        // Parsing span elements, including code spans, character escapes,
        // and inline HTML tags, so that pipes inside those gets ignored.
        $head = $this->parseSpan($head);
        $headers = preg_split('/ *[|] */', $head);
        $col_count = count($headers);
        $attr = array_pad($attr, $col_count, '');

        // Write column headers.
        $text = "<table>\n";
        $text .= "<thead>\n";
        $text .= "<tr>\n";
        foreach ($headers as $n => $header) {
            $text .= "  <th$attr[$n]>" . $this->runSpanGamut(trim($header)) . "</th>\n";
        }
        $text .= "</tr>\n";
        $text .= "</thead>\n";

        // Split content by row.
        $rows = explode("\n", trim($content, "\n"));

        $text .= "<tbody>\n";
        foreach ($rows as $row) {
            // Parsing span elements, including code spans, character escapes,
            // and inline HTML tags, so that pipes inside those gets ignored.
            $row = $this->parseSpan($row);

            // Split row by cell.
            $row_cells = preg_split('/ *[|] */', $row, $col_count);
            $row_cells = array_pad($row_cells, $col_count, '');

            $text .= "<tr>\n";
            foreach ($row_cells as $n => $cell) {
                $text .= "  <td$attr[$n]>" . $this->runSpanGamut(trim($cell)) . "</td>\n";
            }
            $text .= "</tr>\n";
        }
        $text .= "</tbody>\n";
        $text .= "</table>";

        return $this->hashBlock($text) . "\n";
    }

    protected function doDefLists($text)
    {
        //
        // Form HTML definition lists.
        //
        $less_than_tab = $this->tab_width - 1;

        // Re-usable pattern to match any entire dl list:
        $whole_list_re = '(?>
			(								# $1 = whole list
			  (								# $2
				[ ]{0,' . $less_than_tab . '}
				((?>.*\S.*\n)+)				# $3 = defined term
				\n?
				[ ]{0,' . $less_than_tab . '}:[ ]+ # colon starting definition
			  )
			  (?s:.+?)
			  (								# $4
				  \z
				|
				  \n{2,}
				  (?=\S)
				  (?!						# Negative lookahead for another term
					[ ]{0,' . $less_than_tab . '}
					(?: \S.*\n )+?			# defined term
					\n?
					[ ]{0,' . $less_than_tab . '}:[ ]+ # colon starting definition
				  )
				  (?!						# Negative lookahead for another definition
					[ ]{0,' . $less_than_tab . '}:[ ]+ # colon starting definition
				  )
			  )
			)
		)'; // mx

        $text = preg_replace_callback(
            '{
				(?>\A\n?|(?<=\n\n))
				' . $whole_list_re . '
			}mx',
            array($this, '_doDefLists_callback'),
            $text
        );

        return $text;
    }

    protected function _doDefLists_callback($matches)
    {
        // Re-usable patterns to match list item bullets and number markers:
        $list = $matches[1];

        // Turn double returns into triple returns, so that we can make a
        // paragraph for the last item in a list, if necessary:
        $result = trim($this->processDefListItems($list));
        $result = "<dl>\n" . $result . "\n</dl>";

        return $this->hashBlock($result) . "\n\n";
    }

    protected function processDefListItems($list_str)
    {
        //
        //	Process the contents of a single definition list, splitting it
        //	into individual term and definition list items.
        //
        $less_than_tab = $this->tab_width - 1;

        // trim trailing blank lines:
        $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

        // Process definition terms.
        $list_str = preg_replace_callback(
            '{
			(?>\A\n?|\n\n+)					# leading line
			(								# definition terms = $1
				[ ]{0,' . $less_than_tab . '}	# leading whitespace
				(?!\:[ ]|[ ])				# negative lookahead for a definition
											#   mark (colon) or more whitespace.
				(?> \S.* \n)+?				# actual term (not whitespace).	
			)			
			(?=\n?[ ]{0,3}:[ ])				# lookahead for following line feed 
											#   with a definition mark.
			}xm',
            array($this, '_processDefListItems_callback_dt'),
            $list_str
        );

        // Process actual definitions.
        $list_str = preg_replace_callback(
            '{
			\n(\n+)?						# leading line = $1
			(								# marker space = $2
				[ ]{0,' . $less_than_tab . '}	# whitespace before colon
				\:[ ]+						# definition mark (colon)
			)
			((?s:.+?))						# definition text = $3
			(?= \n+ 						# stop at next definition mark,
				(?:							# next term or end of text
					[ ]{0,' . $less_than_tab . '} \:[ ]	|
					<dt> | \z
				)						
			)					
			}xm',
            array($this, '_processDefListItems_callback_dd'),
            $list_str
        );

        return $list_str;
    }

    protected function _processDefListItems_callback_dt($matches)
    {
        $terms = explode("\n", trim($matches[1]));
        $text = '';
        foreach ($terms as $term) {
            $term = $this->runSpanGamut(trim($term));
            $text .= "\n<dt>" . $term . "</dt>";
        }

        return $text . "\n";
    }

    protected function _processDefListItems_callback_dd($matches)
    {
        $leading_line = $matches[1];
        $marker_space = $matches[2];
        $def = $matches[3];

        if ($leading_line || preg_match('/\n{2,}/', $def)) {
            // Replace marker with the appropriate whitespace indentation
            $def = str_repeat(' ', strlen($marker_space)) . $def;
            $def = $this->runBlockGamut($this->outdent($def . "\n\n"));
            $def = "\n" . $def . "\n";
        } else {
            $def = rtrim($def);
            $def = $this->runSpanGamut($this->outdent($def));
        }

        return "\n<dd>" . $def . "</dd>\n";
    }

    protected function doFencedCodeBlocks($text)
    {
        //
        // Adding the fenced code block syntax to regular Markdown:
        //
        // ~~~
        // Code block
        // ~~~
        //
        $less_than_tab = $this->tab_width;

        $text = preg_replace_callback(
            '{
				(?:\n|\A)
				# 1: Opening marker
				(
					(?:~{3,}|`{3,}) # 3 or more tildes/backticks.
				)
				[ ]*
				(?:
					\.?([-_:a-zA-Z0-9]+) # 2: standalone class name
				|
					' . $this->id_class_attr_catch_re . ' # 3: Extra attributes
				)?
				[ ]* \n # Whitespace and newline following marker.
				
				# 4: Content
				(
					(?>
						(?!\1 [ ]* \n)	# Not a closing marker.
						.*\n+
					)+
				)
				
				# Closing marker.
				\1 [ ]* (?= \n )
			}xm',
            array($this, '_doFencedCodeBlocks_callback'),
            $text
        );

        return $text;
    }

    protected function _doFencedCodeBlocks_callback($matches)
    {
        $classname = &$matches[2];
        $attrs = &$matches[3];
        $codeblock = $matches[4];
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);
        $codeblock = preg_replace_callback(
            '/^\n+/',
            array($this, '_doFencedCodeBlocks_newlines'),
            $codeblock
        );

        if ($classname != "") {
            if ($classname[0] == '.') {
                $classname = substr($classname, 1);
            }
            $attr_str = ' class="' . $this->code_class_prefix . $classname . '"';
        } else {
            $attr_str = $this->doExtraAttributes($this->code_attr_on_pre ? "pre" : "code", $attrs);
        }
        $pre_attr_str = $this->code_attr_on_pre ? $attr_str : '';
        $code_attr_str = $this->code_attr_on_pre ? '' : $attr_str;
        $codeblock = "<pre$pre_attr_str><code$code_attr_str>$codeblock</code></pre>";

        return "\n\n" . $this->hashBlock($codeblock) . "\n\n";
    }

    protected function _doFencedCodeBlocks_newlines($matches)
    {
        return str_repeat(
            "<br$this->empty_element_suffix",
            strlen($matches[0])
        );
    }

    //
    // Redefining emphasis markers so that emphasis by underscore does not
    // work in the middle of a word.
    //
    protected $em_relist = array(
        ''  => '(?:(?<!\*)\*(?!\*)|(?<![a-zA-Z0-9_])_(?!_))(?![\.,:;]?\s)',
        '*' => '(?<![\s*])\*(?!\*)',
        '_' => '(?<![\s_])_(?![a-zA-Z0-9_])',
    );
    protected $strong_relist = array(
        ''   => '(?:(?<!\*)\*\*(?!\*)|(?<![a-zA-Z0-9_])__(?!_))(?![\.,:;]?\s)',
        '**' => '(?<![\s*])\*\*(?!\*)',
        '__' => '(?<![\s_])__(?![a-zA-Z0-9_])',
    );
    protected $em_strong_relist = array(
        ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<![a-zA-Z0-9_])___(?!_))(?![\.,:;]?\s)',
        '***' => '(?<![\s*])\*\*\*(?!\*)',
        '___' => '(?<![\s_])___(?![a-zA-Z0-9_])',
    );

    protected function formParagraphs($text)
    {
        //
        //	Params:
        //		$text - string to process with html <p> tags
        //
        // Strip leading and trailing lines:
        $text = preg_replace('/\A\n+|\n+\z/', '', $text);

        $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

        //
        // Wrap <p> tags and unhashify HTML blocks
        //
        foreach ($grafs as $key => $value) {
            $value = trim($this->runSpanGamut($value));

            // Check if this should be enclosed in a paragraph.
            // Clean tag hashes & block tag hashes are left alone.
            $is_p = !preg_match('/^B\x1A[0-9]+B|^C\x1A[0-9]+C$/', $value);

            if ($is_p) {
                $value = "<p>$value</p>";
            }
            $grafs[$key] = $value;
        }

        // Join grafs in one text, then unhash HTML tags.
        $text = implode("\n\n", $grafs);

        // Finish by removing any tag hashes still present in $text.
        $text = $this->unhash($text);

        return $text;
    }

    //## Footnotes

    protected function stripFootnotes($text)
    {
        //
        // Strips link definitions from text, stores the URLs and titles in
        // hash references.
        //
        $less_than_tab = $this->tab_width - 1;

        // Link defs are in the form: [^id]: url "optional title"
        $text = preg_replace_callback(
            '{
			^[ ]{0,' . $less_than_tab . '}\[\^(.+?)\][ ]?:	# note_id = $1
			  [ ]*
			  \n?					# maybe *one* newline
			(						# text = $2 (no blank lines allowed)
				(?:					
					.+				# actual text
				|
					\n				# newlines but 
					(?!\[.+?\][ ]?:\s)# negative lookahead for footnote or link definition marker.
					(?!\n+[ ]{0,3}\S)# ensure line is not blank and followed 
									# by non-indented content
				)*
			)		
			}xm',
            array($this, '_stripFootnotes_callback'),
            $text
        );

        return $text;
    }

    protected function _stripFootnotes_callback($matches)
    {
        $note_id = $this->fn_id_prefix . $matches[1];
        $this->footnotes[$note_id] = $this->outdent($matches[2]);

        return ''; // String that will replace the block
    }

    protected function doFootnotes($text)
    {
        //
        // Replace footnote references in $text [^id] with a special text-token
        // which will be replaced by the actual footnote marker in appendFootnotes.
        //
        if (!$this->in_anchor) {
            $text = preg_replace('{\[\^(.+?)\]}', "F\x1Afn:\\1\x1A:", $text);
        }

        return $text;
    }

    protected function appendFootnotes($text)
    {
        //
        // Append footnote list to text.
        //
        $text = preg_replace_callback(
            '{F\x1Afn:(.*?)\x1A:}',
            array($this, '_appendFootnotes_callback'),
            $text
        );

        if (!empty($this->footnotes_ordered)) {
            $text .= "\n\n";
            $text .= "<div class=\"footnotes\">\n";
            $text .= "<hr" . $this->empty_element_suffix . "\n";
            $text .= "<ol>\n\n";

            $attr = "";
            if ($this->fn_backlink_class != "") {
                $class = $this->fn_backlink_class;
                $class = $this->encodeAttribute($class);
                $attr .= " class=\"$class\"";
            }
            if ($this->fn_backlink_title != "") {
                $title = $this->fn_backlink_title;
                $title = $this->encodeAttribute($title);
                $attr .= " title=\"$title\"";
            }
            $num = 0;

            while (!empty($this->footnotes_ordered)) {
                $footnote = reset($this->footnotes_ordered);
                $note_id = key($this->footnotes_ordered);
                unset($this->footnotes_ordered[$note_id]);
                $ref_count = $this->footnotes_ref_count[$note_id];
                unset($this->footnotes_ref_count[$note_id]);
                unset($this->footnotes[$note_id]);

                $footnote .= "\n"; // Need to append newline before parsing.
                $footnote = $this->runBlockGamut("$footnote\n");
                $footnote = preg_replace_callback(
                    '{F\x1Afn:(.*?)\x1A:}',
                    array($this, '_appendFootnotes_callback'),
                    $footnote
                );

                $attr = str_replace("%%", ++$num, $attr);
                $note_id = $this->encodeAttribute($note_id);

                // Prepare backlink, multiple backlinks if multiple references
                $backlink = "<a href=\"#fnref:$note_id\"$attr>&#8617;</a>";
                for ($ref_num = 2; $ref_num <= $ref_count; $ref_num++) {
                    $backlink .= " <a href=\"#fnref$ref_num:$note_id\"$attr>&#8617;</a>";
                }
                // Add backlink to last paragraph; create new paragraph if needed.
                if (preg_match('{</p>$}', $footnote)) {
                    $footnote = substr($footnote, 0, -4) . "&#160;$backlink</p>";
                } else {
                    $footnote .= "\n\n<p>$backlink</p>";
                }

                $text .= "<li id=\"fn:$note_id\">\n";
                $text .= $footnote . "\n";
                $text .= "</li>\n\n";
            }

            $text .= "</ol>\n";
            $text .= "</div>";
        }

        return $text;
    }

    protected function _appendFootnotes_callback($matches)
    {
        $node_id = $this->fn_id_prefix . $matches[1];

        // Create footnote marker only if it has a corresponding footnote *and*
        // the footnote hasn't been used by another marker.
        if (isset($this->footnotes[$node_id])) {
            $num = &$this->footnotes_numbers[$node_id];
            if (!isset($num)) {
                // Transfer footnote content to the ordered list and give it its
                // number
                $this->footnotes_ordered[$node_id] = $this->footnotes[$node_id];
                $this->footnotes_ref_count[$node_id] = 1;
                $num = $this->footnote_counter++;
                $ref_count_mark = '';
            } else {
                $ref_count_mark = $this->footnotes_ref_count[$node_id] += 1;
            }

            $attr = "";
            if ($this->fn_link_class != "") {
                $class = $this->fn_link_class;
                $class = $this->encodeAttribute($class);
                $attr .= " class=\"$class\"";
            }
            if ($this->fn_link_title != "") {
                $title = $this->fn_link_title;
                $title = $this->encodeAttribute($title);
                $attr .= " title=\"$title\"";
            }

            $attr = str_replace("%%", $num, $attr);
            $node_id = $this->encodeAttribute($node_id);

            return
                "<sup id=\"fnref$ref_count_mark:$node_id\">" .
                "<a href=\"#fn:$node_id\"$attr>$num</a>" .
                "</sup>";
        }

        return "[^" . $matches[1] . "]";
    }

    //## Abbreviations ###

    protected function stripAbbreviations($text)
    {
        //
        // Strips abbreviations from text, stores titles in hash references.
        //
        $less_than_tab = $this->tab_width - 1;

        // Link defs are in the form: [id]*: url "optional title"
        $text = preg_replace_callback(
            '{
			^[ ]{0,' . $less_than_tab . '}\*\[(.+?)\][ ]?:	# abbr_id = $1
			(.*)					# text = $2 (no blank lines allowed)	
			}xm',
            array($this, '_stripAbbreviations_callback'),
            $text
        );

        return $text;
    }

    protected function _stripAbbreviations_callback($matches)
    {
        $abbr_word = $matches[1];
        $abbr_desc = $matches[2];
        if ($this->abbr_word_re) {
            $this->abbr_word_re .= '|';
        }
        $this->abbr_word_re .= preg_quote($abbr_word);
        $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);

        return ''; // String that will replace the block
    }

    protected function doAbbreviations($text)
    {
        //
        // Find defined abbreviations in text and wrap them in <abbr> elements.
        //
        if ($this->abbr_word_re) {
            // cannot use the /x modifier because abbr_word_re may
            // contain significant spaces:
            $text = preg_replace_callback(
                '{' .
                '(?<![\w\x1A])' .
                '(?:' . $this->abbr_word_re . ')' .
                '(?![\w\x1A])' .
                '}',
                array($this, '_doAbbreviations_callback'),
                $text
            );
        }

        return $text;
    }

    protected function _doAbbreviations_callback($matches)
    {
        $abbr = $matches[0];
        if (isset($this->abbr_desciptions[$abbr])) {
            $desc = $this->abbr_desciptions[$abbr];
            if (empty($desc)) {
                return $this->hashPart("<abbr>$abbr</abbr>");
            } else {
                $desc = $this->encodeAttribute($desc);

                return $this->hashPart("<abbr title=\"$desc\">$abbr</abbr>");
            }
        } else {
            return $matches[0];
        }
    }
}
